P0420

P0420
TWC Efficiency Below Threshold (cylinder 1-3)
TWC conversion too low (cylinder 1-3)

P0430
TWC Efficiency Below Threshold (cylinder 4-6)
TWC conversion too low (cylinder 4-6)

Function
In this process, the oxygen absorbtion efficiency of the Three Way Catalytic Converter (TWC) is established through comparison with the oxygen sensor amplitudes before and after the TWC.
If the oxygen absorbtion efficiency of the TWC is greatly diminished because of aging, voltage amplitudes will also develop at the oxygen sensors after the TWC.

Diagnosis conditions
Monitoring of the TWC efficiency is active only when the following conditions are met:
- Oxygen sensing is active.
- RPM and engine load are within specified values.
- No excessive load of the Evaporative Emission (EVAP) Canister
- 350 sec. have past since engine start-up.
- Oxygen sensors, adaptation limits, misfire rate, Mass Air Flow Sensor, Air Flow Sensor Potentiometer, and fuel tank ventilation must not be stored as faults in the Diagnostic Fault Code (DTC) Memory.





Diagnostic procedure
Connect scan tool and advance to menu point "DTC memory".
1. Connect scan tool with adapter cable.
2. Switch ignition on.
3. Initiate diagnosis and advance to menu point "DTC memory"
4. Read DTC memory.

- If other faults are in memory: Erase DTC memory and road test.

Erase DTC memory, followed by road test.
1. Read DTC memory.
2. Repair any faults per Diagnostic Trouble Code Charts.
3. Erase DTC memory.
4. Road test vehicle until TWC temperature is above 300°C (engine has to run for some time with large air volume). Afterwards perform TWC diagnosis when the engine load is between 0.6 and 1.7 ms/rev. and engine rpm is between 2800 1/min. During this procedure, the conditions must exist for at least 350 sec. (time recording is cumulative).
5. Again read DTC memory.

- If no fault: End.
- If DTC P0422: Replace TWC.

Replace Three Way Catalytic (TWC) Converter.
1. Replace TWC as per Repair Manual.
2. Road test as described under 2.
3. Read DTC memory.

- End.